Ignition apparatus



April 23, 1940. R. T. HURLEY IGNITION APPARATUS Filed Sept. 24, 1936 ymw 4m Patented Apr. 23, 1940 UNITED STATES IGNITION Roy T. Hurley, HobbsMMZSQ 7 ENT APPARA'EUS Ferry, N. W2, assignor to Bendix AviationCorporation, douth Bend, Ind, a corporation of Delaware ApplicationSeptember 24, 1936, Serial No. 102,298

5 Claims.

This invention relates to ignition apparatus and more particularly tospark plugs and radio shielding means associated therewith adapted foruse in the ignition systems of internal combustion engines.

Spark plugs and shielding means of the same general type or character asthose comprehended by the present invention'have been heretoforeproposed but insuperable difficulties have been experienced in providinga radio shielded plug which may be readily assembled and disassembled,which is capable of being quickly installed and removed from an engineand the shielding harness provided thereon, and which may beinexpensively manufactured. Furthermore, in the design and constructionof similar spark plugs a great amount of time and thought has been spentby a great many skilled engineers, but without complete success, inattempting to increase the heat dissipation qualities of the plugs inorder to reduce the burning of the electrodes, to obviate pre-ignition,to prevent burning of the insulation on current conducting cablesconnected to the terminals of the plug, and to generally increase thelife and improve the operating characteristics of the plugs.

It is accordingly an object of the present invention to provide a novelradio shielded spark plug which is more reliable and efficient inoperation than similar spark plugs heretofore provided and which may bereadily and inexpensively manufactured.

Another object of the invention is to provide a novel radio shieldingconnection for usebetween a spark plug and conductor conduits of theshielding harness of an internal combustion engine. I

Still another object is to provide novel means in a radio shieldedignition circuit for electrically connecting an insulated conductor andthe center electrode of a spark plug.

A further object is to provide a novel radio shielded spark plug whichmaybe readily and quickly connected in and disconnected from a shieldedignition circuit of an internal combustion engine.

A still further object is to provide a novel combination of a radioshielded spark plug with a shielding connecting elbow which isconstituted by a small number or comparatively rugged parts which are soconstructed and assembled that the possibility of failure due tovibration, jarring, etc., is minimized.

Another object of the invention is to provide a novelspark plug which isso constructed as to combine effective radio shielding with better heatand electrical conductivity characteristics than have been heretoforeprovided.

The above and further objectsand novel features of the invention willmore fully appear from the following detailed description when thevs'ameis read in connection with 'the accompanying drawing. It is to beexpressly understood, however, that the drawing is designed for thepurpose of illustration only and is not intended to define the limits ofthe invention, reference being primarily had for this latter purpose tothe a pended claims.

In the drawing, wherein like reference characters refer to like partsthroughout the several views,

Fig. l is a side elevation, partly in section and with parts brokenaway, of one form of a spark plug embodying the present invention; rFig. 2 is a similar view, partly in section andv with parts broken away,of a second embodiment;

Fig. 3 is a detail sectional view, on an enlarged scale, of the threadedconnection between the spark plug and the shielding elbow showing thecoupling nut in unlocked position; and,

Fig. 4 is a similar view showing said coupling nut in locked position.

In the embodiment of the invention illustrated a against a soft metallicwasher it having high 3 heat conductivity and positioned on an interiorshoulder of the shield to thereby provide a gastight joint between saidshell and nut. Projecting upwardly from nut l4 and preferably formedintegrally therewith is a barrel it having a somewhat larger bore thanthat provided in nut I 4,

said bore being lined with an insulating sleeve ll of mica or othersuitable insulating material.

The upper edge of said barrel is peened over at ltd for the purpose ofholding saidinsulation in position.

In the form shown, center electrode H3 is surrounded by an expansibletube or sleeve l8 of soft metal such as copper and said sleeve issurrounded by and insulated from nut M by a mica cigarette H9. The lowerenlarged end or head 20 of electrode i3 is supported close to groundedelectrode 12 and is spaced from the lower end of nut M by a stack ofmica washers 2 l. Said center electrode extends upwardly into the boreofbarrel 46, H and the upper end thereof is counter-sunk and peenedoutwardly or upset to engage a metallic washer 22 which constitutes apart of the center electrode and bears against a stack of mica washers23. In assembling the paratively rugged, easily assembled parts andbeing adapted to be secured to a spark plug for soldered or brazedtogether.

2 parts last described, cigarette l9 and'sleeve II! are first insertedin the bore of nut l4 and said sleeve is expanded by means of a mandrelto thereby press cigarette is into close engagement with the inner wallsof nut 14 to prevent leakage oi. gases of combustion from the enginecylinder. Electrode I3 has a drive fit in copper sleeve I 8 and thespark gap between the lower end thereof and electrode i3 is adapted tobe readily adjusted by bending the prongs l2a of electrode l3.

Novel simplified means are provided for readily and quickly detachingand connecting an insulated high tension conductor to center electrodei3 and for radio shielding said conductor, said means comprising only asmall number of compivotal or swivel movement relative thereto. In theform-illustrated in Fig. 1, such means includes a hollow, moldedinsulator, one end 24 of which by a cone-shaped shoulder 26. Sleeve 24,25

preferably made of an asbestos Bakelite compound or any other suitableinsulating material and the bore in the arcuate portion is somewhatlarger than the bore in the straight portion thereof, the large andsmall bores being joined by a tapered or conical bore.

Surrounding the smaller or lower portion 24 of insulator 24, 25 adjacentshoulder 26 is a metallic shielding sleeve 21 that is shaped to engagesaid shoulder and has an external flange 28 which is adapted to be heldin firm engagement with and in any position relative to the upper end ofbarrel i6, ita by means of a coupling nut 29 that has threadedengagement with said barrel. An arcuate metallic sleeve 30 surroundsportion 25 of the insulator, the same being adapted to be placed thereonafter the insulator is molded, and is secured to sleeve 2'! by anysuitable means, the sleeves in the form shown having engaging flanges 3iand 32 thereof A bored coupling member 32 is permanently secured to theouter end of sleeve 30, such as by silver soldering, and insulator 24,25 is preferably cemented in radio shielding sleeve 2?, 3G by means ofsome suitable cement, such as ball clay silicate of soda cement. Sleeves2i and 30 may, of course, be detachably secured to one another, ifdesired.

For the purpose of electrically connecting an insulated high tensionconductor 33 to center electrode 83, insulator portion 24 is centrallybored for slidably receiving a conducting bolt 34, while flexibleconductor 33 extendsthrough a preferably larger bore in portion 25 ofthe insulator and is detachably and electrically connected to said boltby means of a tapered nut 35. The latter is soldered or otherwisesuitably secured to conductor 33 and is adapted to thread- I edly engagethe inner end of bolt 34, the axis of the threaded bore of said nutbeing substantially a continuation of the longitudinal axis of conductor33. In the embodiment illustrated, portions of the braided conductor 33are led through sulator 24 and is thus'held in yielding engageshieldingelbow from a magneto or othe'rsource of high tension electric currentthrough a shielding conduit comprising a braided metallic tube 38 whichencloses a coiled metallic spring 39 and is surrounded by an insulatingcovering such as synthetic rubber, for example. The end of tube 38 isflared outwardly and secured between ex-- temal flanges on a pair ofmetallic ferrules 4| and 42 and the conduit assembly is detachablyconnected to elbow 21, 30 by means of a nut 43 which threadedly engagescoupling member 32 and is rotatable relative to said ferrules. Ayieldable washer 44 is shown interposed between coupling member 32 andthe end of shielding conduit 38, 40. To facilitate the insertion ofinsulated conductor 33 into insulator 24, 25, the opening at the outerend of coupling member 32 is conical, as is also nut 35.

In the embodiment of the invention illustrated in Figs. 2 to 4,inclusive, wherein primed reference numerals are employed to indicateparts which are similar and correspond to parts in Fig. 1 that bear thesame reference numerals, insulator 24', is molded in a one-piecemetallic elbow 21', with a small conducting wire 34' therein. Wire 34'is preferably quite stiif, such as piano wire, so that the same will notbe displaced during the pouring of the molten Bakelite intothe mold. Oneend of said wire is adapted to engage or may be integral with a spring31' and the other end, which extends into a coimtersunk bore in elbowportion 25' of the insulator, is secured such as by silver soldering toan externally threaded member 45 that is adapted to be engaged by aninternally threaded nut secured in any suitable manner to the end ofinsulated conductor 33'. To connect and disconnect member and nut 35',either elbow El, 30', when the same is disconnected from barrel it, orconductor 33' may be rotated, depending upon which is the moreconvenient under the particular circumstances. Conductor 33' ispreferably led from a. suitable source of high tension electric currentthrough a suitable shielduseful life of the plug and cable insulation aswell as the operating efiiciencyof the plug, to increase the electricalconductivity of the shielding, and to insure that the various elementsof the assembly will not become loose during operation, novel means areprovided for threadedly connecting certain of said elements. Only theconnection between elbow 21', 30' and barrel 16' will be described indetail, but it will be understood that the same type of thread means maybe employed-at H, at the connection 32', 43 and between nut I4 and bodyIt). In the form shown, the threads on barrel l6 have symmetrical sidefaces 46 and 41 which have an included angle of approximately thirtydegrees, the outer surfaces 48 of the threads, i. e., the major diameterof the threaded portion of the barrel, being cyclindrical. The surface49 at the minor diameter of the barrel, i. e., between the bases of thethreads, is tapered or inclined at a small angle to the axis of thebarrel. On nut 29' similar threads are formed, except that the surface50 of the threads thereon is tapered or inclined relative to the axis ofthe nut and the surface 5| at the base of the thread on the nut iscylindrical.

Thus, when nut 29' is being screwed on and off of barrel IS, the samerotates freely, the parts assuming the relative positions shown in Fig.3. When, howeverpthe internal shoulder of said nut engages flange 28 andis further rotated, the tapered or conical thread surface 50 of the nutmoves into wedging engagement with the conical surface 49 of the barrel,and as the elastic compression on these conical surfaces is increased byrotation of the nut, the thrust faces and. 52 of the barrel and nut,respectively, come into contact. erted by the faces against faces 49increases the frictional resistance therebetween and accordinglyincreases the resistance of the nut to rotation. Vibration and jarringof the parts tends rather to tighten than to loosen the grip between nut29 and barrel "5', thereby insuring that the parts will not become looseduring operation. The close, firm engagement between faces 49, 50 and46, 52 also insures better heat and electrical conductivity, the formerbeing particularly important in the spark plug and the latter beinghighly important both in the plug and the shielding. A better gas sealis also provided and less accuracy is required in cutting the threads onthe cooperating parts than has been heretofore necessary with othertypes of threads.

There is thus provided a novel shielded spark plug in combination with aradio shielding elbow and a shielded conductor, the parts of which areadapted for ready and inexpensive manufacture and are so constructed asto provide a ready and efficient means for detachably and electricallyconnecting an electric current-carrying, radioshielded cable to thecentral electrode of the plug. Novel means are also provided forsecuring. the plug in an engine cylinder and for securing the variousparts of the plug and elbow assembly together, whereby gas leakage isreduced, the rate of heat conduction from the inner to the outerportions of the plug and heat dissipation to the atmosphere arematerially increased, the resistance to flow of current to groundthrough the radio shielding and the plug is materially reduced, and theloosening of parts due to vibration, jarring, etc., is substantiallyeliminated. The novel combination provided also comprises only a smallnumber of comparatively rugged parts which are adapted to be readily andquickly assembled and disassembled for installation, cleaning, andrepair.

Although only two embodiments of the invention have been illustrated anddescribed in detail, it is to be expressly understood that the same isnot limited thereto but that various changes may be made therein, suchas in the design and arrangement of parts illustrated, without departingfront the spirit and scope of invention, as will now be apparent tothose The compressing force ex I skilled in the art. For a definition ofthe limits of the invention, reference will be had primarily to theappended claims.

What is claimed is:

1. In apparatus of the class described, an insulator having a non-linearbore therethrough, a conductor extending into one end of said insulator,said conductor being threaded at the inner end thereof and having anenlarged portion adjacent the other end, a yieldable conducting memberhaving a portion thereof interposed between said enlarged portion andthe end of said insulator, an insulated conductor extending into theother end of said insulator, and means secured to said insulatedconductor and adapted to threadedly engage the threaded portion of saidfirst-named conductor.

2. In apparatus of the class described, a metallic elbow, insulatingmaterial lining said elbow, a conductor extending partially through saidinsulating material from one end thereof and having a threaded portion,a second conductor extending partially through said insulating materialfrom the other end thereof, and an internally threaded member secured tosaid second conductor and adapted to threadedly engage said first-namedconductor, the axis of the bore of said internally threaded member beingsubstantially a continuation of the longitudinal axis of saidsecond-named conductor.

3. In apparatus of the class described, a rigid insulating elbow havinga bore therethrough, a flexible insulated conductor extending into oneend of said bore, a tapered nut secured to said conductor and adapted toseat against a tapered wall portion of said bore, and a conductorextending into the other end of said bore and having a threaded portionadapted to be threadedly engaged by said nut.

4. In apparatus of the class described, a rigid insulator having a boretherethrough, the axis of a portion of said bore being arcuate, aconductor extending into said bore and having means thereon to limit themovement thereof into said bore, a flexible conductor extending into thearcuate portion of said bore, and means secured to said flexibleconductor for detachably electrically connecting the adjacent ends ofsaid conductors together.

5; In a spark plug having a center electrode and a barrel portionextending above said electrode to form a socket, the combinationtherewith of a metallic sleeve, means for detachably connecting saidsleeve to said barrel, insulating means in said sleeve having a portionextending into said barrel, an electric current carrying conductorextending through a portion of said insulating means, means including ayieldable connection for electrically connecting said conductor andelectrode, an insulated conductor extending into said insulating means,and a member secured to said insulated conductor for threadedly engagingsaid first-named conductors.

6. In apparatus of the class described, a rigid shielding elbow having abore there through, electrical conductors extending into opposed ends ofsaid elbow, one of said conductors having means thereonto limit themovement thereof into said bore, and means for detachably connectingadjacent ends of said conductors to each other within said elbow,whereby neither of said conductors may be withdrawn from said elbow.

ROY T. HURLEY.

